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Patented Feb. 5, 1929.

UNITED STATES PATENT OFFICE.

CHARLES F. BOOTH AND ARTHUR B. GERBER, OF ANNISTON, ALABAMA, ASSIGNORS TO FEDERAL PHOSPHORUS COMPANY, OF BIRMINGHAM, ALABAMA, A CORPORA- TION OF ALABAMA.

NEUTRAL TRISODIUM PHOSPHATE.

Application filed July 19, 1924. Serial No. 726,918.

This invention relates to a new compound of sodium phosphate of a composition daffering from that of ordinary tri-sodium phosphate. and preferably produced by the 7 (Na PO .12H O) NaOH. According to the equation i would seem as if 10.5# NaOH would be suflicient to convert the di-sodium phosphate to tri-sodium phosphate on a basis of 100# of the latter; however, an average of several years operation is approximately 15#Na()H instead of the theoretical figure.

The presence of this additional quantity of caustic in ordinary tri-sodium phosphate may be determined by a titration of the crystals. An examination of numerous samples from various manufacturers gave an average of 0.535 for a relation or ratio of the titration of the phenolphthalein to a titration of the same quantity of the methyl orange end point. This ratio is derived by dividing the cubic centimeters of standard acid used for the phenolphthalein titration, by the sum of the cubic centimeters standard acid used for the methyl orange titration. For example, if a given quantity of ordinary tri-sodium phosphate required 3.75 cc. half normal hydrochloric acid for the pheuolphthalein titration and 3.25 cc. half normal hydrochloric acid for the methyl orange titration the ratio would be 0.535. The formula for such a compound would correspond to 7(Na PO .12H ()).Na()H. It was during the experiments conducted with a view to reducing the quantity of caustic soda required that it was found tri-sodium could be produced with a formula Ntl;;I O .l2P. as generally applied to tri-sodium phosphate. From the titration method as outlined above, it was apparent that the two compounds were of different composition and accordingly trisodium phosphate, as now generally made, is an alkaline tri-sodium phosphate, while our new compound is a neutral tri-sodium phosphate.

In the production of this neutral tri-sodium phosphate the variations of specific gravity require corresponding variations of the ratio to produce neutral tri-sodium phosphate. In the chart the crystallization area curves A-B, CD illustrate in area M how if the specific gravity is too high with reference to the ratio some di-sodium phosphate will be formed, while in area 0 it is shown how if the ratio is too high withreference to the specific gravity some alkaline trisodium phosphate will be formed. The area N indicates the conditions under which the neutral tri-sodium phosphate will form.

Area N lies between curves A 1%, along" specific gravity ratios from 1.30. ratio 0.425 and 1.30 specific gravity, ratio 0.450: and curve C I), along specific gravity 1.308. ratio 0.395 and 1.39 specific gravity, ratio 0.445.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent, is

1. The hereindescribed new composition of matter, consisting of a tri-sodium phosphate having no free alkali.

2. The hereindescribed new composition of matter, consisting of tri-sodium phosphate in crystalline form, in which the result of titration shows a ratio of 0.5 between the phenolphthalein end point and methyl orange end point.

3. The hereindes ribed new combination of matter, consisting of tri-sodium phosphate in crystalline form, containing no free alkali.

In testimony whereof we atlix our signa tures.

CHARLES F. BOOTH. ARTHUR B. GERBER. 

